1. Field of the Invention
The present invention relates generally to endoscopic surgical instruments. More particularly, the invention relates to an improved push rod assembly portion of an endoscopic surgical instrument having bipolar endoscopic cautery capability.
2. State of the Art
Endoscopic surgery is widely practiced throughout the world today and its acceptance is growing rapidly. In general, endoscopic/laparoscopic surgery involves one or more incisions made by trocars where trocar tubes are left in place so that endoscopic surgical tools may be inserted through the tubes. A camera, magnifying lens, or other optical instrument is often inserted through one trocar tube, while a cutter, dissector, or other surgical instrument is inserted through the same or another trocar tube for purposes of manipulating and/or cutting the internal organ. Sometimes it is desirable to have several trocar tubes in place at once in order to receive several surgical instruments. In this manner, organ or tissue may be grasped with one surgical instrument, and simultaneously may be cut with another surgical instrument; all under view of the surgeon via the optical instrument in place in the trocar tube.
Various types of endoscopic surgical instruments are known in the art. These instruments generally comprise a slender tube containing a push rod which is axially movable within the tube by means of a handle or trigger-like actuating means. An end effector is provided at the distal end of the tube and is coupled to the push rod by means of a clevis so that axial movement of the push rod is translated to rotational or pivotal movement of the end effector. End effectors may take the form of scissors, grippers, cutting jaws, forceps, and the like.
Modern endoscopic procedures often involve the use of electrocautery, as the control of bleeding by coagulation during surgery is critical both in terms of limiting loss of blood and in permitting a clear viewing of the surgical site. As used herein, cautery, electrocautery, and coagulation are used interchangeably. Several types of electrocautery devices for use in endoscopic surgery are described in the prior art. Monopolar electrosurgical instruments employ the instrument as an electrode, with a large electrode plate beneath and in contact with the patient serving as the second electrode. High frequency voltage spikes are passed through the instrument to the electrode (i.e., end effector) of the endoscopic instrument to cause an arcing between the instrument and the proximate tissue of the patient. The current thereby generated continues through the patient to the large electrode plate beneath the patient. Monopolar cautery has the disadvantage that the current flows completely through the patient. Because control of the current path through the body is not possible, damage can occur to tissue both near and at some distance from the surgical site. In addition, it is has been observed that monopolar cautery can result in excessive tissue damage due to the arcing between the end effector and the tissue.
In order to overcome the problems associated with monopolar cautery instruments, bipolar instruments have been introduced. In bipolar electrosurgical instruments, two electrodes which are closely spaced together are utilized to contact the tissue. Typically, one end effector acts as the first electrode, and the other end effector acts as the second electrode, with the end effectors being electrically isolated from each other and each having a separate current path back through to the handle of the instrument. Thus, in a bipolar instrument, the current flow is from one end effector electrode, through the tissue to be cauterized, to the other end effector electrode.
Various endoscopic instruments with cautery capability are known in the art. U.S. Pat. No. 4,418,692 to Guay, for example, discloses a device for use in laparoscopic tubal cauterization for blocking the Fallopian tubes of a patient. The device comprises a substantially tubular body member having a spring-biased piston slidably mounted therein. A pair of electrodes (either monopolar or bipolar) are disposed to grasp living tissue when the piston is in a first position biased by the spring and to release the tissue when a button is pressed which moves the piston into a second position. The device includes a circuit breaker which interrupts current flowing to the electrodes when the piston is in the second position. When the electrodes grasp the tissue, however, current is supplied to the entire surface of the electrode, that is, both the grasping surface and the outer non-grasping surface.
Another electrosurgical instrument for use in combination with an endoscope is disclosed in U.S. Pat. No. 5,007,908 to Rydell for "Electrosurgical Instrument Having Needle Cutting Electrode and Spot-Coag Electrode". Rydell's device includes an elongated flexible tubular member with a plurality of lumens. The distal end of the tubular member is provided with a bullet shaped ceramic tip covered with a conductive layer and having an opening coupled to a first one of the lumens. The conductive layer is coupled to a conductor which extends through a second one of the lumens to an electrical source. A second conductor, also coupled to the electrical source is slidable through the first lumen by a plunger. The two electrodes form a bipolar pair. In a second embodiment, the conductive layer on the ceramic tip is split by an insulating gap and both halves of the tip form a bipolar pair of electrodes. As with the Guay device, above, substantially the entire distal surface of Rydell's device serves as an electrode when energized.
Several hemostatic bipolar electrosurgical scissors have also been described. U.S. Pat. No. 3,651,811 to Hildebrandt describes a bipolar electrosurgical scissors having opposing cutting blades forming active electrodes. The described scissors enables a surgeon to sequentially coagulate the blood vessels contained in the tissue and then to mechanically sever the tissue with the scissor blades. In particular, with the described bipolar electrosurgical scissors, the surgeon must first grasp the tissue with the scissor blades, energize the electrodes to cause hemostasis, de-energize the electrodes, and then close the scissor blades to sever the tissue mechanically. The scissors are then repositioned for another cut accomplished in the same manner. With the bipolar electrosurgical scissors of Hildebrandt, the surgeon cannot maintain the electrodes in a continuously energized state because the power supply would be shorted out and/or the blades damaged if the blades are permitted to contact each other while energized.
The disadvantages of the bipolar scissors of Hildebrandt are overcome by the disclosure in U.S. Pat. Nos. 5,324,289 and 5,330,471 to Eggers. In its preferred embodiment, the bipolar electrosurgical scissors of Eggers comprise a pair of metal scissor blades which are provided with an electrically insulating material interposed between the shearing surfaces of the blades so that when the scissor blades are closed, the metal of one blade never touches the metal of the other blade; i.e., the insulating material provides the cutting edge and the shearing surface. With the arrangement provided by Eggers, a cautery current will pass from the top back edge of the bottom metal blade through the tissue which is to be cut and to the bottom back edge of the top metal blade directly in advance of the cutting action. As the scissors are gradually closed, the hemostasis preferentially occurs at a location just in advance of the cutting point which itself moves distally along the insulated cutting edges of the blades in order to sever the hemostatically heated tissue. With this arrangement, the scissors may be maintained in a continuously energized state while performing the cutting. The Eggers patent describes various alternative embodiments of the bipolar scissors, including the use of metal blades with only one blade being insulated on its shearing surface, and the use of insulating blades with back surfaces coated with metal.
In all of the bipolar instruments, and particularly in double acting instruments such as scissors, safe and effective delivery of the cautery current to the end effectors is always a difficult engineering problem. In particular, it is difficult to deliver a bipolar current source within the limited space in which endoscopic surgery is performed. It is necessary to assure that the conductors delivering the current are well insulated from each other, that they are easily connected to the end effectors, and that they are easily connected to a standard source of bipolar cautery current. Both Rydell et al. (U.S. Pat. No. 5,258,006) and Eggers (U.S. Pat. No. 5,330,471) have proposed bipolar push rod arrangements. Eggers has proposed a bifurcated cylindrical push rod in which two halves of the push rod are conductive and which are both covered with an insulating material. Rydell et al. has proposed a pair of conductive leads which extend through a double lumen silastic or polyurethane push rod. Neither of the bipolar push rod arrangements is easy to implement, and neither has been commercially successful. Moreover, the arrangement taught by Rydell et al. cannot be used with pivoting double acting end effectors as is required in the art of interest.